Fixed and live visualization of RNAs in Drosophila oocytes and embryos

•smFISH and genetically encoded fluorescent RNA tagging provide complementary tools to visualize RNA in situ.•smFISH provides quantitative detection of transcripts at high resolution with particular advantages for Drosophila oocytes.•Fluorescent RNA tagging in transgenic Drosophila allows dynamic analysis of RNA through live imaging.•Both methods allow multiplexing and can be combined with protein visualization. The ability to visualize RNA in situ is essential to dissect mechanisms for the temporal and spatial regulation of gene expression that drives development. Although considerable attention has been focused on transcriptional control, studies in model organisms like Drosophila have highlighted the importance of post-transcriptional mechanisms - most notably intracellular mRNA localization - in the formation and patterning of the body axes, specification of cell fates, and polarized cell functions. Our understanding of both types of regulation has been greatly advanced by technological innovations that enable a combination of highly quantitative and dynamic analysis of RNA. This review presents two methods, single molecule fluorescence in situ hybridization for high resolution quantitative RNA detection in fixed Drosophila oocytes and embryos and genetically encoded fluorescent RNA labeling for detection in live cells.